The assignee of the present invention designs and manufactures spacecraft for communications and broadcast services. Such spacecraft are frequently required to undergo orbit transfer from a first orbit to a second orbit. For example, the spacecraft may undergo orbit raising from an initial orbit (into which the spacecraft is disposed by a launch vehicle, for example) to an operational orbit.
Such spacecraft may be equipped with on board propulsion systems, including chemical or electric thrusters, for orbit raising from a launch vehicle transfer orbit (or “parking orbit”) to an operational orbit, for example, to a geosynchronous orbit, as well as for stationkeeping once disposed in the operational orbit, and for attitude control/momentum management purposes.
Spacecraft propulsion systems generally include thrusters, which may be broadly categorized as either “chemical” or “electric” based on the respective primary energy source. Chemical thrusters suitable for spacecraft propulsion systems may deliver relatively high thrust of 10-1000 newtons, for example, substantially irrespective of spacecraft power limitations, but such thrusters are generally incapable of operating at a specific impulse (Isp) higher than 500 seconds. Electric thrusters may operate at an Isp of 1000-4000 seconds, but spacecraft power availability typically constrains thrust levels to less than one newton.
It is sometimes desirable to configure two or more spacecraft for simultaneous launch on a single launch vehicle. As disclosed in US patent publication number 2016/0304219, assigned to the assignee of the present invention, two or more spacecraft configured to be launched within a common fairing of the launch vehicle may be configured in a stacked launch configuration where at least a portion of orbit raising is performed with the two or more spacecraft coupled together. One of the stacked spacecraft may provide most or all of the orbit transfer capability for the stack of spacecraft.